This application is a continuation of U.S. application Ser. No. 14/579,602, filed Dec. 22, 2014, now U.S. Pat. No. 9,432,459, which is a is a continuation of U.S. application Ser. No. 14/088,786, filed Nov. 25, 2013, now U.S. Pat. No. 8,918,435, which is a continuation of U.S. application Ser. No. 13/170,031, filed Jun. 27, 2011, now U.S. Pat. No. 8,595,267, which are herein incorporated by reference in their entirety.
Several leading technology organizations are investing in building technologies that sell “software-as-a-service”. Such services provide access to shared storage (e.g., database systems) and/or computing resources to clients, or subscribers. Within multi-tier e-commerce systems, different resources may be allocated to subscribers and/or their applications from whole machines, to CPU, to memory, to network bandwidth, and to I/O capacity.
Database systems managing large amounts of data on behalf of users may distribute and/or replicate that data across two or more machines, often in different locations, for any of a number of reasons, including security issues, disaster prevention and recovery issues, data locality and availability issues, etc. These machines may be configured in any number of ways, including as a shared resource pool.
Interaction between client applications and database servers typically includes read operations (read-only queries), write operations (to store data), and update operations that can be conceptualized using a read-modify-write workflow.
While embodiments are described herein by way of example for several embodiments and illustrative drawings, those skilled in the art will recognize that the embodiments are not limited to the embodiments or drawings described. It should be understood, that the drawings and detailed description thereto are not intended to limit embodiments to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope as defined by the appended claims. The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description or the claims. As used throughout this application, the word “may” is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words “include”, “including”, and “includes” mean including, but not limited to.